The present invention relates generally to an apparatus for reducing noise and vibration transmitted into the passenger compartment of a vehicle from the suspension system.
Rear suspension coiled springs of a motor vehicle have a surge resonance that can be excited typically through a rear drive module and transmitted into the passenger compartment of the vehicle through the rear half-shafts and the rear suspension. Generally very little energy from the rear drive module is required to excite a steel spring at its resonant frequency, typically about 80 Hz. The energy is amplified at this frequency and transmitted into the vehicle where a ‘boom’ period is heard, producing noise during a vibration period.
Attempting to solve the concern by significantly changing the stiffness of the springs can negatively affect the ride characteristics of the vehicle, and simply moves the noise and vibration period to a less desirable place.
Dipping or coating the suspension springs has been used to reduce spring clatter. The coating has some damping effect, but not enough to significantly reduce a surge resonance. A vehicle suspension system may use air springs and eliminate coil springs, but this option introduces a need to provide a continual, reliable source for the air in the air springs.
A need exists in the industry for a technique that separates the exciting frequency from the spring's resonant frequency and attenuates the spring's response prior to the energy being transmitted into the passenger compartment.